Eukaryotes rely on mitochondria to produce ATP efficiently, yet this same organelle is the major source of reactive oxygen species (ROS), an endogenous toxin. Mitochondria! dysfunction has been associated with many disorders including type 2 diabetes, obesity and neurodegenerative diseases. Recent work, including much that was funded previously by this grant, has shown that the PGC-1 transcriptional coactivators link mitochondrial function to the external and extracellular environment in many tissues. This new grant proposes experiments that probe the role of PGC-1 a in normal physiology and in a number of diseases involving mitochondrial dysfunction. Our first Aim will determine the role PGC-1 a in the development of diabetes and obesity in mice, using a muscle-specific KO we have made. Mice will be studied in the basal state and under challenges of high-fat feeding and aging. Glucose homeostasis will be measured with glucose tolerance tests and hyperinsulinemic-euglycemic clamps. We will also study muscle fiber-types and running performance in the presence and absence of PGC-1 a. Our second Aim will be focused on the collaboration in vitro and in vivo between AMP kinase and PGC-1 a. Our new data indicates that AMPK directly phosphorylates PGC-1 a in vitro and in cells, and requires PGC-1 a to modulate certain programs of gene expression. In our third Aim, we have recently found that PGC-1 a has a powerful ability to suppress the formation of ROS, as it activates mitochondrial respiration. Indeed the ability of ROS to induce a ROS detoxification program is dependent on PGC-1 a and PGC-1 p. We will determine the key molecular events that allow ROS to induce PGC-1 a and, conversely, attempt to understand the transcription factors on which PGC-1 a docks to turn on the ROS detoxification program. We will also attempt to create strains of mice with a mutant PGC-1 a gene which can still regulate OXPHOS but not ROS, and study effects in metabolic disease. These studies should provide new opportunities to modulate oxidative metabolism in ways that allow for new approaches to some important human diseases.